Vascular changes following radiation (rad.) include alterations in the intima and formation of vaso-occlusive thrombi. Long term sequelae depend on the magnitude of initial circulatory impairment and regional tissue hypoxia. We have found that irradiation vitro (200 rads) causes selective inhibition of the vascular antithrombotic prostaglandin I2 leaving the platelet (plt.) proaggregatory Thromboxane A2 intact. (Lancet, In Press). We plan to characterize the effects of rad. on arachidonic acid (AA) metabolism in the vessel. Experimentals will be performed in vitro on human umbilical vascular rings, umbilical venous endothelial cell cultures, and in vivo, in rabbits. We will determine whether the decrease in PGI2 is due to inhibition of AA release from cell membrane phospholipids, inhibition of cyclo-oxygenase and/or prostacyclin synthetase, or inactivation of PGI2, and time to recover from these effects. We will evaluate the role of oxygen radical formation in the process, determine whether rad. induced vascular lipid peroxides interfere with AA metabolism, and the role of antioxidants. Assays will include RIA, bioassays, TLC and HPLC. Effects of rad. on plt. function (nucleotide and AA metabolism) and on in vitro plt-endothelial interaction will be studied. In rabbits, unilateral rad. of the head and neck, and infusion of autologous Indium labeled plts. will be used to evaluate the effect of rad. on in vivo plt. endothelial interaction. Radical scavengers, antioxidants, aspirin and dipyridamole will be used to modify any observed abnormalities. Minor aims include effects of radiomimetic drugs (anthracyclines) on AA metabolism, and the effects of rad. on megakaryocytes, and endothelium from the microcirculation. Since hypercholesterolemia enhances the deleterious effect of rad. on vessels, effects of rad. on plts. and endothelial cells made "cholesterol-rich" will also be studied. Thus, the goals of our project include elucidation of biochemical mechanisms involved in rad. effects on vascular platelet interaction, and their modification both in vivo and in vitro. These interactions are of major clinical interest since vascular complications occur post rad. If free radical species cause abnormalities in vascular AA metabolism, the results will be of significance in other states, i.e. aging and inflammation. Since rad. of plts. is often performed prior to plt. transfusion, its effects on plt. metabolism are relevant.